The present invention relates to a solar battery package and a method for making the same.
A solar battery package is known wherein one or a plurality of solar cells or photovoltaic cells each having a light receiving area on one surface thereof are hermetically sealed in a casing.
One conventional solar battery package which is well known in the prior art is shown in a sectional view in FIG. 1 of the accompanying drawings.
Referring first to FIG. 1, the solar cells, generally identified by 10 and, in the instance as shown, electrically connected in series with each other, are placed on a common substrate 11 in a predetermined pattern. The substrate 11 with the solar cells 10 thereon has a pair of lead wires 13 which extend outwards from the series-connected solar cells 10. The substrate 11 so constructed is mounted on a base support 15 by the use of a bonding agent 14 with the lead wires 13 inserted into and soldered to terminal pins 16 which are secured to and extend outwards from the base support 15. A transparent covering 17 is mounted on the base support 15 with its inside surface thereof spaced from the solar cells 10 on the substrate 11.
In the conventional solar battery package of the construction shown in FIG. 1, the casing constituted by the base support 15 and the transparent covering 17 is made of a synthetic resin such as acrylic resin or polycarbonate resin. When the casing is made of acrylic resin, it has been found that, because of insufficient physical strength of such resin, cracking is liable to occur during the outdoor use of the solar battery for a long period of time. Specifically, portions of the base support 15 where the terminal pins 16 are connected tend to be susceptible to cracking and, once this cracking occurs, a liquid medium, such as water, can penetrate into the space defined between the base support and the transparent covering. When this happens it causes a reduction in performance of the solar cells.
In addition, since the acrylic resin tends to deform in shape when heated to about 90.degree. C or more, the solar battery or batteries packed in such a casing made of acrylic resin may not be used during the summer season, or in tropical areas, in which bright sunlight is likely to cause the casing to be heated to a temperature approximating or in excess of the temperature at which the acrylic resin starts to deform.
Moreover, because the method of making the solar battery package is complicated and the construction requires the use of manual labor, particularly in making various connections by the use of one or more kinds of bonding agents and, therefore, the solar battery package of the kind described above is not suited for mass production and, if production is not impossible, tends to become expensive.
In order to obviate the above described drawbacks resulting from the use of acrylic or polycarbonate resin as a material for the casing, and also to make it possible to manufacture solar battery packages on a mass production scale, I have tried to use, in place of the acrylic resin and the polycarbonate resin, a silicone resin and an epoxy resin which are known as a coating material for the conventional solar battery package. However, it has been found that the silicone resin, though it exhibits a relatively low water absorbability, tends to allow humidity to permeate therethrough and, therefore, the use of this silicone resin as a material for the battery casing may result in reduction in performance of the solar cells due to humidity permeating into the interior of the casing. Moreover, since the silicone resin when used alone has insufficient physical strength required to support the solar cells which are fragile, a casing made of the silicone resin requires the employment of an additional support or reinforcement in order to protect the solar cells. Furthermore, since the silicone resin tends to be easily electrostatically charged enough to attract dust particles floating in the air, the available output power of the solar battery package, if the casing is made of this silicone resin, tends to be less because substantially none of the light incident upon the casing reaches the light receiving areas of the solar cells in the presence of the dust particles electrostatically attracted on the casing.
Because of the foregoing reasons, silicone resin is not suited as a material for a battery casing which is used outdoors for a substantial period of time, particularly during the life time of the solar cells.
Shown in FIG. 2 is a solar battery package I have devised. Referring now to FIG. 2 the solar cells 10 are shown to be embedded in a transparent block 17 of silicone resin by the use of a molding technique, which block 17 is sandwiched between transparent glass plates 18 held flat against the upper and lower surfaces of the block 17. The assembly, composed of the block 17, having the solar cells 10 embedded therein, and the glass plates 18, is mounted on a frame 19 made of stainless steel and having a shape similar to the shape of the assembly. Between the inside surface of the frame 19 and the outer periphery of the assembly is a sealing material 20. However, I have found that the construction shown in FIG. 2 is complicated and requires a time-consuming labor in applying the sealing material and that the solar battery package shown in FIG. 2 is not suited for mass production.
In the construction shown in FIG. 2, the use of epoxy resin in place of the silicone resin has been tried. However, although epoxy resin has excellent physical properties as compared with silicone resin, it has been found that, due to water absorbability, the epoxy resin forming the block 17 tends to separate from the solar cells 10 during the use of the battery package for a long period of time and that epoxy resin when exposed to the sun, particularly to ultraviolet rays, for a long period of time tends to be easily colored so that the transparency is consequently reduced to such an extent that the available output voltage is reduced. Therefore, the use of epoxy resin as a material for the block 17 has been found to be unsatisfactory. Therefore, the solar battery package I have devised as shown in FIG. 2 does not constitute the subject matter of the present invention.